In the security printing industry a major concern is presented by the use of colour photocopiers by counterfeiters to produce counterfeit documents from security documents. One means of alleviating such counterfeiting would be to incorporate into a security document areas of bright metallic printing because a colour photocopier is unable to accurately reproduce such printing due to certain known, inherent limitations of colour photocopiers themselves (bright gold surfaces are reproduced as yellow and bright silver surfaces are reproduced as grey). However, to date, all attempts in the industry to produce a metallic intaglio ink, which will successfully print a long-lasting metallic image having a bright and shiny appearance, have failed.
Previously introduced metallic inks for intaglio printing have been unable to achieve a bright and shiny appearance and, instead, appear dull and are ineffective. This is because intaglio printed wide lines have a naturally uneven, irregular surface which, combined with the dulling effect of the intaglio ink extender (which is a normal constituent of intaglio inks), results in a yellow or grey colour rather than a highly reflective, bright metallic colour. The printing press properties (i.e. pertaining to ink flow and transfer and plate wiping) of such previously introduced inks has also proven to be poor.
Accordingly, there has been a long-standing need in the industry for a metallic intaglio ink which can produce through intaglio printing a stable (long-lasting), bright, reflective metallic image.